Over the past few years, thermoplastic elastomer polymers, such as polyether ester amide and polyester amide TPE-As, have been widely used in the field of sports shoes, in particular for constituting soles of shoes, for their good mechanical properties, in particular their spring-back property.
In such applications, the soles of sports shoes are made of at least two layers, often one made of TPE-A (in particular of PEBAX®) and the other made of TPE-PU, these two layers being adhesively assembled.
In general, TPE substrates are assembled by adhesion to the other substrates by means of a primer and of adhesives or glues comprising organic solvents, also known as solvent-based primers or solvent-based adhesives, these primers and these adhesives are generally two-component polyurethane adhesives. The two-component adhesives comprise a first component which is an organic resin or a mixture of organic resins comprising functions that can react with the second (crosslinking) component consisting of an isocyanate or of a mixture of isocyanates in solution at least in an organic or pure solvent. By way of examples, the resins constituting the first component may be polyesters, acrylics or epoxy resins comprising hydroxylated, carboxylated, epoxy, amine or amide reactive functions, in solution in an organic solvent, and a second (crosslinking) component which is a solution of isocyanate in an organic or pure solvent.
The conventional assembly process comprises the following successive steps:
Preparation of Substrates S1 and S2:
                Cleaning: the surfaces to be bonded are cleaned, in general, with an organic solvent, in particular methyl ethyl ketone (abbreviated to MEK); the solvent evaporates off during drying, thus involving waste given off into the atmosphere;        Application of a primer: a solvent-based two-component polyurethane-based primer layer is applied, in general with a brush, to the surface, of the substrates, that is to be bonded; the whole is then placed in an oven in order to dry the primer, this step again involving solvent emissions into the atmosphere;        Application of an adhesive: a layer of solvent-based or water-based, two-component polyurethane adhesive is applied, in general with a brush, to the substrates prepared; the whole is placed in an oven, generating further emission of solvent into the atmosphere when a solvent-based adhesive is used.Assembly of Substrates S1 and S2:        
The two substrates S1 and S2 that have thus been adhesive-coated are assembled and undergo a pressing operation in order to ensure their adhesion.
During these various steps, it has been evaluated that approximately 30 kg of organic solvents originating from the use of a solvent-based primer and of a solvent-based adhesive are emitted during the assembly of 10 000 shoes. For this reason, it will be desirable to use primers and/or adhesives that are less polluting in order to limit the solvent emissions while having multilayer structures for which the adhesion between the layers of substrate S1 and S2, defined above, is compatible with use in the field of shoe soles.